The present invention relates to a process for producing a urethane elastomer by a one shot method. More particularly, it relates to a process for molding a urethane elastomer having excellent properties in a short cycle by a one shot method.
It has been proposed to produce urethane elastomers having suitable properties by reacting an organic polyisocyanate with (1) a chain polyol having a molecular weight of 400 to 5,000 and (2) an aromatic diamine.
In the process for producing a urethane elastomer by a one shot method, the components used as the starting materials are chemically stable and have lower viscosity in comparison with those of the urethane prepolymer, whereby the operation can be effectively performed especially in the casting operation using a casting apparatus.
In accordance with the conventional one shot method, the pot-life is advantageously shorter than that of the prepolymer method. However, there are disadvantages that a tendency of a phase separation is found after gelation and the reaction velocity decreases and an initial strength is slowly imparted to take a long time from the injection to the mold-separation (mold-separable period). Accordingly, the casting processibility is good, nevertheless, the casting cycle could not be shortened disadvantageously.
When a large amount of a catalyst is used in order to shorten the mold-separable period, the pot-life is remarkably shortened to make trouble in the casting and the physical properties of the shaped product especially an ageing deterioration resistance is decreased.